"increase the strength" is correct and usable in written English.
You can use it to describe an action or a process. For example, "The athlete worked hard to increase the strength in her legs."
Digoxin and digitoxin are commonly prescribed to increase the strength of heart contraction.
It called for the West to increase the strength of its conventional military forces.
The most common reason for alloying is to increase the strength of a metal.
There was a repeater in a black plastic briefcase, which would increase the strength of Byron's body transmitter.
She continues to train using gymnastics -- on the parallel bars, high bar, rings -- to increase the strength in her shoulders.
"This is the explanation for the Sisyphean efforts to increase the strength and capabilities of the army.
The first is to increase the strength of the magnetic field at two locations along the field line.
These parts are light, corrosion-resistant, and (if alloy is used) can be heat treated to appreciably increase the strength.
Likewise, an emphasis on information technology can increase the strength of the force while it reduces the need for manpower, the single most expensive aspect of today's military.
Un-supplemented RRWs neither increase the strength nor the stiffness of the MFs.
Superlinear preference functions increase the strength of the 'rich-get-richer' effect.
